Strain hardening is a natural consequence of most working and forming
operations on aluminium and its alloys. In pure aluminium and the
non-heat-treatable aluminium-manganese and aluminium-magnesium alloys,
strain hardening increases the strengths achieved through solid solution
and dispersion hardening...
Strain hardening is a natural consequence of most working and forming
operations on aluminium and its alloys. In pure aluminium and the
non-heat-treatable aluminium-manganese and aluminium-magnesium alloys,
strain hardening increases the strengths achieved through solid
solution and dispersion hardening.
Work hardening is used extensively to produce strain hardened tempers
of the non-heat-treatable alloys. The temper designation system,
according to ANSI H35.1(M), is shown bellow.
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F
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As-fabricated.
Applies to the product of shaping processes in which no special
control over thermal conditions or strain-hardening is employed.
For wrought products, there are no mechanical property limits.
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O
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Annealed.
Applies to wrought products which are annealed to obtain the
lowest strength temper, and to cast products which are annealed
to improve ductility and dimensional stability. The O may be
followed by a digit other then zero.
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H
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Strain hardened (wrought products only).
Applies to products which have their strength increased by
strain hardening, with or without supplementary thermal treatments
to produce some reduction in strength. The H is always followed
by two or more digits.
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The first digit following the H indicates the specific combination of
basic operations, as follows:
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H1
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Strain hardened only.
Applies to products which are strain – hardened to obtain the
desired strength without supplementary thermal treatment.
The number following this designation indicates the degree of
strain hardening.
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H2
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Strain hardened and partially annealed.
Applies to products which are strain – hardened more than the
desired final amount and then reduced in strength to the desired
level by partial annealing. For alloys that age-soften at room
temperature, the H2 tempers have the same minimum ultimate tensile
strength as the corresponding H3 tempers. For other alloys, the H2
tempers have the same minimum ultimate tensile strength as the
corresponding H1 tempers and slightly higher elongation. The number
following this designation indicates the degree of strain – hardening
remaining after the product has been partially annealed.
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H3
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Strain hardened and stabilized.
Applies to products which are strain – hardened and whose
mechanical properties are stabilized either by a low temperature
thermal treatment or as a result of a heat introduced during
fabrication. Stabilization usually improves ductility.
This designation is applicable only to those alloys which,
unless stabilized, gradually age-soften at room temperature.
The number following this designation indicates the degree of
strain-hardening remaining after the stabilization treatment.
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The digit following the designations H1, H2 and H3 indicates the
degree of strain hardening.
Numeral 8 has been assigned to indicate tempers having an ultimate
tensile strength equivalent to that achieved by a cold reduction
(temperature during reduction not to exceed 50oC) of approximately
75 percent following a full anneal.
Tempers between O (annealed) and 8 are designated by numerals 1
through 7. Material having an ultimate tensile strength about midway
between that of the O temper and that of the 8 temper is designated
by the numeral 4; about midway between the O and 4 tempers by the
numeral 2; and about midway between 4 and 8 tempers by the numeral 6.
Numeral 9 designates tempers whose minimum ultimate tensile strength
exceeds that of the 8 temper by 10 MPa or more. For two–digit H
tempers whose second digit is odd, the standard limits for strength
are the arithmetic mean, rounded to the nearest multiple of 5 MPa of
the standard limits for the adjacent two digit H tempers whose second
digit are seven.
The third digit, when used, indicates a variation of a two–digit
temper. It is used when the degree of control of temper or the
mechanical properties or both differ from, but are close to, that
(or those) for the two–digit H temper designation to which it is
added, or when some other characteristic is significantly affected.